E34 Rear Suspension Noise

[Jean]

This noise was present before and now after replacing ALL of the following:

- all 4 trailing arm bushings (had a shop press the old ones out and press new oem bushings in)
- new subframe bushings pressed in with the factory tool
- front + 2 side diff bushings
- rear upper subframe bushing
- rsm's
- lower "dog bone" trailing arm-to-subframe bushing

ALL parts installed were OEM new, Lemf/Meyle HD parts only.

Rear shocks are used Billy HD from e28, used with H&R Sport springs. Upper/lower spring pads present, new bump stops, new RSMs.

All the mounting points have been tightened with a torque wrench per the shop manual, and the trailing arm bushings were torqued t 77Nm with the car Level on the ramps.

Any ideas before I push this car off the cliff?

This noise is present when driving at low/medium speeds, straight or turning (more so). I've been able to duplicate it now by basically pushing down on the trunk area.



I've rulled out it being the exhaust, so it's either something with the trailing arm or subframe or something else I am not seeing...
Anybody?

[Jean]

I should also mention that when I was checking stuff around the driver rear side area (seems to make more noise than the passenger), as I jacked the car up it made the noise. I removed the wheel and put another jack under the trailing arm and as I jacked it up it also made the noise.

Maybe I should disconnect the sway bar and see if that fixes it...hmmm.

[jlevie]

The noise doesn't "ring a bell". Is it still present if you disconnect the shocks from the trailing arms? What about if you disconnect the sways? If the noise is present with the shocks & sways disconnected I'm something is cracked in the subframe, spring perches, diff mounts, etc. If the noise goes away with either the shocks or sways disconnected, look the body side of the relevant parts.

[Jean]

Will do, thanks!

I had the subframe with all the parts out of the car and nothing looked cracked, but maybe the problem is in the body of the car as you are thinking.

I'll disconnect the sway bar and then do the same with rear shock and try again.

[GDA]

Posted also in your other E34 thread... but in listening to this vid got another idea.

Possible heat shield rubbing by the rear diff? The one that sits in front of the tank? Or possibly one of the brake or parking brake cables is binding up on one of the upper heat shields.

[Jean]

Thanks! I'll disconnect the brace and/or dog bones along with the rear sway next. I'll double check the parking cables as well, they are seated how they should be in the trailing arm tabs.

I did check that heat shields were not in the way, I also used a flashlight and a mirror to check for common things and nothing stood out.

[Jean]

Drove to work today and it made no noises, and I've made no changes since yesterday. Just like yesterday it needed a few miles to start making these noises, not sure what to think, possibly rubber bushings or shocks start doing this after a couple of miles of use...

Tomorrow after work I'll get it back on the lift and remove rear shocks/ sway bar for inspection.

[German Audio Specialties]

Man...wish you were closer.

I own a "Chassis Ears" kit, which is a set of headphones connected to a black box that contains a switch and an amplifier, with 6 selectable, color-coded inputs.

Each of the 6 inputs has a 15' cord with a color-coded alligator clip at the end, which has a piezo microphone in it. You clip the clips on where you suspect the noise is, bundle the cables safely, pop the headphones on and select which of the 6 mics is picking it up best...such an awesome diagnostic tool for such things!

Tell you what, buddy, if you cannot find the noise next time you are under it, let me know, I will ship my chassis ears to you.

Luke

[Jean]

Luke,

Funny thing you mention this tool. I was basically "picturing" something similar in my head, multiple mics and visual screen on the laptop showing one with highest volume.... basically the same thing!

After work tomorrow I'll remove the rear sway, remove the back seat, and re-inspect or re-assemble rear shock/spring combo.

I should probably inspect the long bolts that hold the subframe under the seat as well...

[Jean]

This morning on the way to work it was silent, and as the car sat in the parking lot as soon as I left it started making these noises.

Problem solved guys. After work went to a shop while it was making these awful noises and put it on the rack, disconnected the dog bones and noise is gone. Pushed the car down a few times, it's silent and smooth. Just got home after driving it for about 10 miles, these noises are 100% gone. I'll report back tomorrow as well once it sits overnight and all.

I installed new dog bones right after I bought this car, so I think they "might" still be under warranty. Right now I am just driving w/o them as all they aren't critical, it's the same suspension as on e30, plus these dog bones that limit the "droop" for the trailing arms. I'll install new ones next week still.

[1craze30]

How'd this work out?

[Jean]

It was the rear pitman arms.

[Onizukachan]

FYI, they are necessary on the e34, as they limit the toe change under load (cornering).
unless you go to KMAC RTABs with do away with them b/c the kmacs have much less flex than the oem bushings.

[Jean]

e28, e32, e34 suspension = teh suck.